Video streaming or progressive download is a popular application within the Internet. A video streaming client connected via an ISP (Internet Service Provider); e.g. a mobile or fixed operator, requests a streaming server, located somewhere within the ISP network or outside in the Internet, to send a video stream. One of the protocols that can be used is HTTP over TCP/IP. In contrast to accessing a web page or to traditional video downloading, the video client starts displaying the content of the requested file before the entire source file has been downloaded successfully by the client. Video content transmission in IP networks is affected by the transport characteristics of the underlying transmission networks, such as bandwidth, delay, jitter and packet loss. The end user perception will be impaired by initial buffering, i.e. the time from the request until the playout of the video file will start, but also from video stalling during the playout followed by rebuffering as soon as the receiver buffer in the client application has drained completely and no further content is available. This is usually the case when the provided average bandwidth by the transport network is lower than the video stream bit rate. A buffer emulator inside the monitoring system is required that calculates the buffer level and provides further information about the rebuffering characteristics.
Known video monitoring algorithms tend, however, to be complex, and require frequent deep packet inspections (DPI) on the bit stream in order to acquire the needed information about the video or they require the original video source in order to perform a comparison between monitored video and original video. Such solutions are not feasible for network monitoring probe systems, which have to analyze thousands of sessions in parallel and in real time, due to the computational capacity that such a task would require.